Refrigeration cycle apparatus

ABSTRACT

A refrigerant cycle apparatus comprising: 
     a compressor  1 , a radiator  2 , decompression means  3 , a heat absorber  4 , an internal heat exchanger  5  that performs heat exchange between a refrigerant at an outlet of said radiator and the refrigerant at an outlet of said heat absorber, wherein first temperature detection means  30  for detecting a refrigerant temperature between an outlet of the compressor  1  and an inlet of the radiator  2  and second temperature detection means  31  for detecting the refrigerant temperature between the outlet of the radiator  2  and a high-pressure side inlet of the internal heat exchanger  5  are provided, and an opening degree of decompression means  3  is controlled so that a temperature difference (ΔT) between a detection temperature by the first temperature detection means  30  and the detection temperature by the second temperature detection means  31  becomes a target value.

TECHNICAL FIELD

The present invention relates to a refrigeration cycle apparatus usingan internal heat exchanger, more particularly to a refrigerant controlfor stably securing performance.

BACKGROUND ART

Descriptions will be given to prior art as follows.

Conventionally, a hot water supply apparatus is proposed as a built-inrefrigeration cycle apparatus such as:

a hot water supply apparatus comprising a refrigeration cycle includinga compressor, a hot water supply heat exchanger, an electronic expansionvalve, and a heat source side heat exchanger whose heat source is anexternal air, and a hot water supply cycle including a hot water supplyheat exchanger and a hot water supply tank,

wherein since ability control means that uses an ability-variable typecompressor and ability-controls the compressor in response to changes inexternal environment conditions of the heat source side heat exchangeris attached, expansion valve opening degree control means forcontrolling an opening degree of an electronic expansion valve so as tomake a discharge temperature of a compressor to be a target value inresponse to changes in external environment conditions (an externaltemperature, for example) of the heat source side heat exchanger androtation speed control means for controlling a rotation speed of thecompressor to be a target value in response to changes in the externalenvironment conditions of the heat source side heat exchanger areattached, an opening of the electronic expansion valve is controlled soas to make the discharge temperature of the compressor becomes a targetvalue in response to changes in the external environment conditions (anexternal temperature, for example) of the heat source side heatexchanger, and the rotation speed of the compressor is controlled to bea target value in response to changes in the external environmentconditions of the heat source side heat exchanger, an optimal operationcondition can be obtained in which a hot water supply ability and a hotwater supply load further match, and a coefficient of performance (COP)can be improved and down-sizing of elements such as an heat exchangerbecomes possible. (For example, refer to Patent Document 1)

A water heater is also proposed such as:

a water heater for heating a hot water supply fluid in a supercriticalheat pump cycle where a refrigerant pressure in a high pressure sidebecomes equal to or more than the critical pressure of the refrigerantcomprising:

a compressor,

a radiator that performs heat exchange between a refrigerant dischargedfrom the compressor and a hot water supply fluid and is configured sothat a refrigerant flow and the hot water supply fluid flow opposes,

a decompressor for decompressing the refrigerant flowing out of theradiator, and

an evaporator that makes the refrigerant that flows out of thecompressor evaporate, makes the refrigerant absorb a heat to dischargeit into a suction side of the compressor,

wherein a refrigerant pressure of a high-pressure side is controlled sothat a temperature difference (ΔT) between the refrigerant that flowsout of the radiator and the hot water supply fluid that flows thereinbecomes a predetermined temperature difference (ΔTo). (For example,refer to Patent Document 2) In this example of the prior art, a heatexchange efficiency of the radiator can be enhanced to improveefficiency of a heat pump.

[Patent Document 1] Japanese Patent Gazette No. 3601369 (pp. 6; FIG. 1)

[Patent Document 2] Japanese Patent Gazette No. 3227651 (pp. 1-3; FIG.2)

SUMMARY OF INVENTION Problems to be Solved by the Invention

Both of the above examples of the prior art control refrigerantconditions so that a discharge temperature of the compressor or atemperature difference (ΔT) between the refrigerant that flows out ofthe radiator and the hot water supply fluid that flows therein becomes atarget value to achieve an efficient operation. However, there was aproblem that in the vicinity where an efficiency (COP) of therefrigeration cycle becomes maximum, a control based only on an inletside (the above discharge temperature) of the radiator or an outlet side(the above temperature difference ΔT) is difficult to achieve stable andefficient operation conditions because changes in the dischargetemperature or the temperature difference ΔT are small. In addition,since an operation in which an internal heat exchanger exists in therefrigerant circuit is not considered, there was a problem that tocontrol to achieve stable and efficient operation conditions isdifficult.

The present invention is made to solve the above problems in the priorart. The object is to obtain a refrigeration cycle apparatus capable ofstably achieving efficient operation conditions by controlling operationvalues based on standard conditions of the radiator and outletconditions of the radiator to be a target value.

Means for Solving the Problems

In order to solve the above problems, the refrigeration cycle apparatusaccording to the present invention includes at least a compressor, aradiator, decompression means capable of changing an open degree, a heatabsorber, an internal heat exchanger that performs heat exchange betweena refrigerant at an outlet of the radiator and the refrigerant at theoutlet of the heat absorber. The refrigeration cycle apparatus ischaracterized in that at least first refrigerant conditions detectionmeans for detecting standard conditions of the radiator and secondrefrigerant conditions detection means for detecting refrigerantconditions between an outlet of the radiator and a high-pressure sideinlet of an internal heat exchanger are provided, and an opening degreeof decompression means is controlled so that a calculation valuecalculated based on an output of the first refrigerant conditionsdetection means and the output of the second refrigerant conditionsdetection means becomes a target value.

EFFECT OF THE INVENTION

According to the present invention, the expansion valve opening degreeis controlled so that the COP becomes maximum based on standardconditions of the radiator and refrigerant conditions of the radiatoroutlet part, so that a refrigerant cycle apparatus capable of stablyachieving efficient operation can be obtained.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing a configuration of a refrigeration cycleapparatus according to Embodiment 1 of the present invention.

FIG. 2 is a diagram showing an operation behavior on a P-h diagramaccording to Embodiment 1 of the present invention.

FIG. 3 is a diagram showing a temperature distribution of a refrigerantand water in a water heat exchanger according to Embodiment 1 of thepresent invention.

FIG. 4 is a diagram showing cycle conditions against an expansion valveopening degree according to Embodiment 1 of the present invention.

FIG. 5 is a diagram showing changes in each calculation value, heatingability, and COP against an expansion valve opening degree according toEmbodiment 1 of the present invention.

FIG. 6 is a diagram showing changes in other calculation value, heatingability, and COP against an expansion valve opening degree according toEmbodiment 1 of the present invention.

FIG. 7 is a diagram showing a control flowchart according to Embodiment1 of the present invention.

FIG. 8 is a diagram showing a refrigeration cycle apparatus according toEmbodiment 2 of the present invention.

FIG. 9 is a diagram showing an operation behavior on a P-h diagramaccording to Embodiment 2 of the present invention.

DESCRIPTIONS OF CODES AND SYMBOLS

-   1 compressor-   2 radiator (water heat exchanger)-   3 expansion valve-   4 heat absorber (evaporator)-   5 internal heat exchanger-   20 hot water supply side pump-   21 hot water storage tank-   22 use side pump-   23, 24, 25 on-off valve-   29 blower-   30, 31, 32, 33, 41, 42, 52 temperature detection means-   35, 51 pressure detection means-   40 controller-   50 heat source apparatus-   60 hot water storage apparatus

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1

Descriptions will be given to a refrigerant cycle apparatus byEmbodiment 1 according to the present invention.

FIG. 1 shows a configuration diagram of the refrigerant cycle apparatusaccording to the present embodiment. In the figure, the refrigerantcycle apparatus according to the present embodiment is a hot watersupply apparatus using carbon dioxide (hereinafter, CO₂) as arefrigerant, composed of a heat source apparatus 50, a hot water storageapparatus 60, and a controller 40 for controlling these. The presentembodiment shows an example of the hot water supply apparatus, however,it is not limited thereto. The apparatus may be an air conditioner. Inthe same way, the refrigerant is not limited to carbon dioxide but anHFC refrigerant may be used.

The heat source apparatus 50 is composed of a compressor 1 forcompressing the refrigerant, a radiator 2 (hereinafter, referred to“water heat exchanger”) for taking out heat of a high-temperaturehigh-pressure refrigerant compressed in the compressor 1, an internalheat exchanger 5 for further cooling the refrigerant output from thewater heat exchanger 2, a decompressor 3 (hereinafter, referred to“expansion valve”) that decompresses the refrigerant and whose openingdegree can be changed, an heat-absorber 4 (hereinafter, referred to“evaporator”) for evaporating the refrigerant decompressed in theexpansion valve 3, and an internal heat exchanger 5 for further heatingthe refrigerant flowed out of the evaporator 4. That is, the internalheat exchanger 5 is a heat exchanger that heat-exchanges the refrigerantat an outlet of the water heat exchanger 2 with the refrigerant at theoutlet of the evaporator 4. A blower 29 is provided for sending air onan outer surface of the evaporator 4. There are also provided firsttemperature detection means 30 for detecting a discharge temperature ofthe compressor 1, second temperature detection means 31 for detecting anoutlet temperature of the water heat exchanger 2, fifth temperaturedetection means 32 for detecting an inlet refrigerant temperature of theevaporator 4, and sixth temperature detection means 33 for detecting asuction temperature of the compressor 1. In addition, the firsttemperature detection means 30 and the second temperature detectionmeans 31 correspond to a first refrigerant conditions detection meansand second refrigerant conditions detection means respectively in anexample of control in FIG. 7 to be described later.

A hot water storage apparatus 60 is connected with the water heatexchanger 2, which is a radiator, via piping, being composed of a heatsource side pump 20, a hot water storage tank 21, a use side pump 22,and on-off valves 23, 24, 25. Here, on-off valves 23, 24, 25 may be asimple valve only for switching operation or an opening variable valve.When a water level of the hot water storage tank 21 drops, the on-offvalves 24, 25 are closed, the on-off valve 23 is opened, and hot waterstorage operation is performed in which supplied water is heated up to apredetermined temperature. When a heat dissipation loss is large and thetemperature in the hot water storage tank 21 decreases such as inwinter, the on-off valves 23, 25 are closed, the on-off valve 24 isopened, and circulation heating operation is performed in whichlow-temperature hot water in the hot water storage tank 21 is re-boiled.At the time of using the hot water supply, the on-off valves 23, 24 areclosed, the on-off valve 25 is opened, the use side pump 22 startsoperation to transfer stored hot water to the use side. At an inlet sideof the water heat exchanger 2, third temperature detection means 41 isattached for detecting an inlet temperature of a medium (water) to beheated. At an outlet side of the water heat exchanger 2, fourthtemperature detection means 42 is attached for detecting the outlettemperature of the medium (water) to be heated.

A controller 40 performs calculation using detected values from firsttemperature detection means 30, second temperature detection means 31,fifth temperature detection means 32, sixth temperature detection means33, third temperature detection means 41, and fourth temperaturedetection means 42 to control an opening degree of the expansion valve3, a rotation speed of the compressor 1, and the rotation speed of thehot water supply side pump 20, respectively.

FIG. 2 is a P-h diagram describing cycle conditions during hot waterstorage operation in the refrigeration cycle apparatus shown in FIG. 1.In FIG. 2, solid lines denote refrigerant conditions at a certainexpansion valve opening degree and A, B, C, D, and E denote refrigerantconditions in the hot water storage operation. At the time of the hotwater storage operation, a high-temperature high-pressure refrigerant(A) discharged from the compressor 1 flows into the water heat exchanger2. In the water heat exchanger 2, the refrigerant heats supplied waterwhile dissipating heat to water circulating the hot water storagecircuit to decrease the own temperature. A refrigerant (B) flowed out ofthe water heat exchanger 2 dissipates heat in the internal heatexchanger 5 to further decrease (C) the temperature, being decompressed(D) by the expansion valve 3 to turn into a low-temperature low-pressurerefrigerant. The low-temperature low-pressure refrigerant absorbs heatfrom the air in the evaporator 4 to evaporate (E). The refrigerantflowed out of the evaporator 4 is heated in the internal heat exchanger5 to turn into a gas (F) and sucked by the compressor 1 to form arefrigeration cycle.

Here, the expansion valve 3 is controlled so that a suction superheatdegree of the compressor 1 becomes a target value (for example, 5 to 10°C.). Specifically, based on a detection value of fifth temperaturedetection means 32 detecting an inlet refrigerant temperature of theevaporator 4, a temperature decrease amount due to a pressure loss inthe evaporator 4 and the internal heat exchanger 5 is corrected, anevaporation temperature (ET) is estimated, a suction superheat degreeSH_(s) is calculated by the following formula using a detection value(T_(s)) of sixth temperature detection means 33 detecting a suctiontemperature of the compressor 1.

SH _(s) =T _(s) −ET

Using the above formula, an opening degree of the expansion valve 3 iscontrolled so that SH_(s) becomes a target value. An example is given inwhich an evaporation temperature (ET) is estimated based on thedetection value of the fifth temperature detection means 32, however, itis not limited thereto. Pressure detection means (second pressuredetection means) 51 (refer to FIG. 1) is installed between alow-pressure side outlet of the internal heat exchanger 5 and the inletof the compressor 1, and from the detection value, a refrigerantsaturation temperature may be obtained. A suction superheat degreecontrol precedes other high efficiency operation control because afunction to prevent liquid return of the compressor 1 precedes afunction to efficiently operate the water heat exchanger 2 from theviewpoint of securing reliability of the equipment.

Next, operation on the P-h diagram in the case when the opening degreeof the expansion valve 3 is made smaller is denoted by broken lines inFIG. 2. When the opening degree of expansion valve 3 is made smaller,the refrigerant flow amount flowing from the expansion valve 3 to theevaporator 4 decreases and the suction superheat degree of thecompressor 1 temporarily increases. In addition, since the refrigerantshifts to a high pressure side, the pressure on the high pressure sideincreases and a discharge temperature becomes high. At the same time, awater heat exchanger output temperature decreases so that a temperaturedifference in the becomes constant. When the water heat exchanger outputtemperature decreases, a heat exchange amount in the internal heatexchanger 5 decreases, and as a result, the suction superheat degreebecomes almost the same state as that of before the opening degree ofthe expansion valve 3 is made smaller to indicate a constant value. Thatis, a change in opening degree of the expansion valve 3 is absorbed bythe heat exchange amount of the internal heat exchanger 5 (the heatexchange amount varies in response to the opening degree of theexpansion valve 3) to make a change in the suction superheat degreesmall. Accordingly, control of the suction superheat degree of thecompressor 1 alone cannot secure heating ability in the water heatexchanger 2 and efficiency is lowered. Therefore, new control isrequired in order to secure heating ability and improve operationefficiency.

Next, descriptions will be given to why a local maximal value occurs inperformance (COP) using a temperature distribution in the water heatexchanger shown in FIG. 3.

FIG. 3 shows a refrigerant and water temperature distribution in thewater heat exchanger 2. In the figure, thick solid lines show a changein refrigerant temperature, and a thin solid lines denote a change inwater temperature. ΔT1 denotes a temperature difference between thewater heat exchanger inlet temperature and water outlet temperature, andΔT2 denotes a temperature difference between the water heat exchangeroutlet temperature and water inlet temperature. ΔTp is a temperaturedifference at a pinch point where the temperature difference between arefrigerant and water in the water heat exchanger 2 becomes minimum. ΔTdenotes a temperature difference between the water heat exchanger inlettemperature and the water heat exchanger outlet temperature. As shown bya cycle state against the expansion valve opening degree in FIG. 4, whena discharge temperature is increased by decreasing the expansion valve 3opening degree, under a condition when heating ability in the water heatexchanger 2 is almost constant, the outlet temperature of the water heatexchanger 2 decreases so that an average temperature difference of therefrigerant and water in the water heat exchanger 2 is maintained, andthe temperature difference ΔTp of pinch point also decreases. Further,as the refrigerant amount shifts to a high pressure side, a dischargepressure rises to increase an input and COP is lowered. To the contrary,when the expansion valve 3 opening degree is made large and thedischarge temperature is lowered, the outlet temperature of the waterheat exchanger 2 increases so that an average temperature differencebetween the refrigerant and water in the water heat exchanger 2 ismaintained. The temperature difference ΔTp at the pinch point alsoincreases, however, a heating ability ratio becomes small and COP islowered. Accordingly, as shown by broken lines in the figure, a suitableexpansion opening degree exists that makes COP maximum.

Next, FIG. 5 shows changes in operation values obtained from thetemperature of each part when the opening degree of the expansion valve3 changes. In FIG. 5, the horizontal axis represents the opening degree(%) of the expansion valve 3, and the vertical axis represents thesuction superheat degree, discharge temperature, temperature differenceΔT2 between the outlet temperature of the water heat exchanger and waterinlet temperature, heating ability ratio, COP ratio. The heating abilityratio and COP ratio show a ratio when a maximum value against theexpansion valve opening degree is set as 100%, respectively. Againstchanges in the opening degree of the expansion valve 3, changes in thesuction superheat degree can be regarded as almost a constant value, sothat it is understood that changes in the heating ability ratio and theCOP ratio cannot be judged by the suction superheat degree. Whencontrolling the COP to be maximum based on the temperature differenceΔT2 between the discharge temperature and the outlet temperature of thewater heat exchanger and water inlet temperature, changes in thedischarge temperature and temperature difference ΔT2 are small in thevicinity of the expansion valve opening degree when the COP reachesmaximum as shown by a dotted line in the figure, so that it is foundthat a high accuracy temperature measurement is required for controllingCOP to be maximum.

Next, FIG. 6 shows changes in other operation values obtained fromtemperatures of each part when the opening degree of the expansion valve3 is changed. In FIG. 6, the horizontal axis represents the openingdegree (%) of the expansion valve 3. The vertical axis represents anoutlet/inlet temperature difference ΔThx of the internal heat exchanger,a temperature difference ΔT between a discharge temperature and anoutlet temperature of the water heat exchanger, a total temperaturedifference ΣΔT of the above ΔT1 and ΔT2, heating ability, and a COPratio, respectively. Characteristics of FIG. 6 shows that operation canbe performed in the vicinity where the COP becomes maximum by eithercontrolling a heat exchange amount of the internal heat exchanger 5based on the temperature difference ΔThx between the outlet and inlet ofthe internal heat exchanger or controlling the heat exchange amount ofthe water heat exchanger 2 based on the total temperature difference ΣΔTof ΔT1 and ΔT2 of the water heat exchanger 2. Further, the temperaturedifference ΔT between the discharge temperature and the outlettemperature of the water heat exchanger significantly changes in thevicinity of the expansion valve opening degree at which the COP becomesmaximum, so that it is understood that a deviation from the maximumvalue of the COP could be controlled to be small based on thetemperature difference ΔT. Here, only the case of the temperaturedifference ΔT is shown, however, the same effect can be expected bycontrolling based on the difference (ΔT1−ΔT2) of the temperaturedifferences ΔT1 and ΔT2.

Thus, it is possible to achieve an operation in the vicinity of themaximum efficiency by adopting a high-pressure side outlet temperatureof the internal heat exchanger 5 for ΔThx, the discharge temperature forΔT, and the discharge temperature and a water side outlet/inlettemperatures for ΣΔT.

As is understood from FIG. 6, a total temperature difference ΣΔT of thetemperature difference ΔT1 between the water heat exchanger inlettemperature and water outlet temperature and the temperature differenceΔT2 between the water heat exchanger outlet temperature and water inlettemperature becomes a minimum. The control based on such an index has aphysical meaning and being reasonable. However, high-precisiontemperature detection is required because change in temperature is smallin the vicinity where the COP becomes a maximum compared with thetemperature difference ΔT. Further, from FIG. 3, it is considered thatwhen the COP becomes a maximum value, a temperature difference ΔTp at apinch point is almost the same as that of ΔT2 between the water heatexchanger outlet temperature and water inlet temperature. This isbecause a maximum performance is shown when two temperature differencesthat become minimum in the water heat exchanger 2 become equal withoutbeing biased to either of them when considering characteristics of theheat exchanger. Accordingly, it is allowable to control the expansionvalve 3 so as to make ΔTp and ΔT2 to be equal.

Next, descriptions will be given to an example of a control operation ofthe refrigeration cycle apparatus of FIG. 1 in which an expansion valveopening degree is controlled so as to make a suction superheat degreeand the above temperature difference ΔT to converge at target values.

FIG. 7 is a flowchart showing a control operation of the refrigerationcycle apparatus. With the present invention, for the purpose of giving apriority to reliability of products, the suction superheat degree (SHs)control of the compressor 1 precedes the temperature difference ΔTcontrol for securing the heating ability.

Firstly, when the suction superheat degree (SHs) is smaller than atarget value (SHm) by a preset convergence range ΔSH or less (S101), theexpansion valve opening degree is lowered until the suction superheatdegree (SHs) converges. Thus, when the suction superheat degree (SHs) issecured, the temperature difference ΔT is made to converge at the targetvalue. Specifically, when the temperature difference ΔT is smaller thana target value (ΔTm) by a preset convergence range δT or less (S102),the expansion opening degree is lowered and ΔT is made to converge.Thus, lower limit values of the suction superheat degree (SHs) and thetemperature difference ΔT can be suppressed.

Next, when the suction superheat degree (SHs) is larger than the targetvalue (SHm) by a preset convergence range ΔSH or more (S103), theexpansion valve opening degree is increased until the suction superheatdegree (SHs) converges. Thus, when the suction superheat degree (SHs) isconverged, the temperature difference ΔT is made to converge at thetarget value. Thus, when the suction superheat degree (SHs) isconverged, the temperature difference ΔT is made to converge at thetarget value. Specifically, when the temperature difference ΔT is largerthan the target value (ΔTm) by a preset convergence range δT or more(S104), the expansion opening degree is increased and ΔT is made toconverge. Thus, upper limit values of the suction superheat degree (SHs)and the temperature difference ΔT can be suppressed. An example is shownin which a priority is given to control the suction superheat degree,however, it is not limited thereto when using a compressor which isresistant to liquid return. The same effect can be expected even whenthe priority order is exchanged. Through the above control, the suctionsuperheat degree (SHs) and the temperature difference ΔT are convergedat target values.

In the above, descriptions are given to an example in which the suctionsuperheat degree (SHs) and the temperature difference ΔT are controlledto converge at target values (SHm, ΔTm), however, it is allowable that,in place of the temperature difference ΔT, a total temperaturedifference ΣΔT of ΔT1 and ΔT2, a difference between ΔT1 and ΔT2(ΔT1−ΔT2), or ΔThx can be used to control them to converge at a targetvalue, respectively. When using ΣΔT and (ΔT1−ΔT2), they are obtained bycalculating detection temperatures by the first temperature detectionmeans 30, the second temperature detection means 31, the thirdtemperature detection means 41, and the fourth temperature detectionmeans 42. When using ΔThx, internal heat exchanger outlet temperaturedetection means 52 is attached (refer to FIG. 1) between a high-pressureside outlet of the internal heat exchanger 5 and an inlet of theexpansion valve 3, the temperature difference ΔThx is obtained from adetection temperatures by the second temperature detection means 31 andthe internal heat exchanger outlet temperature detection means 52.

Since, in the present embodiment, in addition to suction superheatdegree control of the compressor, the expansion valve opening degree ismade to be controlled so that the COP becomes maximum based on atemperature difference ΔT (or ΣΔT, ΔT1−ΔT2, ΔThx) between the dischargetemperature and the water heat exchanger outlet temperature, a highefficiency refrigeration cycle apparatus can be obtained.

A refrigerant saturation temperature (ET) is obtained based on an outputof the fifth temperature detection means 32 or pressure detection means,the suction superheat degree (SHs) is obtained by the detectiontemperature (Ts) of the sixth temperature detection means and therefrigerant saturation temperature (ET), and the expansion valve openingdegree is controlled so that the suction superheat degree (SHs) becomesa target value, so that the superheat degree of the suction part of thecompressor 1 is secured, liquid return to the compressor 1 can beprevented, and reliability can be secured. In the example of FIG. 1,descriptions are given to an example in which the fifth temperaturedetection means 32 is provided between the expansion valve 3 and theevaporator 4, it can be disposed at any position between the inlet ofthe evaporator 4 and a low-pressure side inlet of the internal heatexchanger 5.

In the present embodiment, when controlling the superheat degree and theabove temperature differences (ΔT, ΣΔT, ΔT1−ΔT2, ΔThx), the control ofthe superheat degree precedes the control of the above temperaturedifferences. From this point, the reliability of the compressor 1 issecured.

In the present embodiment, the radiator is composed of the water heatexchanger, so that a high efficiency hot water supply apparatus can beobtained.

Embodiment 2

Descriptions will be given to a refrigeration cycle apparatus accordingto Embodiment 2 of the present invention as follows.

FIG. 8 is a drawing showing a configuration of the refrigeration cycleapparatus according to the present invention. What is different fromEmbodiment 1 is that a first pressure detection means 35 is provided inplace of the first temperature detection means 30 for detecting thedischarge temperature of the compressor 1. Based on the first pressuredetection means 35, a virtual saturation temperature is obtained, whichis a standard condition of the water heat exchanger 2. The pressuredetection means 35 can be shared with a pressure sensor provided, forexample, to prevent an abnormal rise in high pressure. Descriptions onan operation behavior will be omitted because they are the same asEmbodiment 1.

In the present embodiment, like a conventional HFC refrigerant, avirtual superheat degree of the water heat exchanger 2 outlet iscalculated to control the refrigerant conditions thereof. Specifically,from first pressure detection means 35 provided in place of the firsttemperature detection means 30, a virtual saturation temperature iscalculated as a standard condition of the water heat exchanger 2 andfrom the difference between a virtual saturation temperature Tsat andoutlet temperature Tcount of the water heat exchanger 2 detected by thesecond temperature detection means 31, a virtual superheat degree SC isobtained from the following formula.

SC=Tsat−Tcount

In the present embodiment, the opening degree of the expansion valve 3is controlled in the same way as the flowchart of FIG. 7 so that the SCobtained by the above formula becomes a target value (SCm) whoseefficiency is maximum.

Here, how to obtain the virtual saturation temperature will beexplained.

FIG. 9 is a diagram showing an operation behavior of the refrigerationcycle apparatus according to the present invention on a P-h diagram. Thevirtual saturation temperature can be freely defined by demonstrating adefinition such as a pseudo critical temperature trajectory connectingflexion points of isothermal lines like a dashed line α and a verticalline like a dotted line β extended with an enthalpy at a critical pointbeing a constant. However, in order to operate the refrigeration cycleapparatus stably and at the maximum efficiency, a virtual saturationtemperature should be selected under which the temperature differencebecomes large in the vicinity of the maximum efficiency as mentionedabove. Then, the virtual saturation temperature can be obtained as anintersection of a constant pressure line with a pressure at a point B,which is a detection value by first pressure detection means 35 and thedashed line α, or as an intersection of a constant pressure line with apressure at a point B, which is a detection value by first pressuredetection means 35 and the dotted line β.

In the present embodiment, since the virtual saturation temperature isused in place of the discharge temperature of the compressor 1, firsttemperature detection means 30 in FIG. 1 can be omitted and low cost canbe achieved. Like the conventional HFC refrigerant, superheat degree ofthe outlet of the water heat exchanger 2 is controlled, therefore,control of the expansion valve can be applied as it is, which has beenconventionally used.

1. A refrigerant cycle apparatus comprising: at least a compressor, aradiator, decompression means capable of changing an open degree, a heatabsorber, an internal heat exchanger that performs heat exchange betweena refrigerant at an outlet of said radiator and the refrigerant at anoutlet of said heat absorber, wherein first refrigerant conditionsdetection means for detecting standard conditions of at least saidradiator and second refrigerant conditions detection means for detectingrefrigerant conditions between an outlet of said radiator and ahigh-pressure side inlet of said internal heat exchanger are provided,and an opening of said decompression means is controlled so that acalculation value calculated based on at least an output of said firstrefrigerant conditions detection means and the output of said secondrefrigerant conditions detection means becomes a target value.
 2. Therefrigerant cycle apparatus of claim 1 comprising: third temperaturedetection means for detecting an inlet temperature of a medium to beheated and fourth temperature detection means for detecting an outlettemperature of the medium to be heated, wherein the opening degree ofsaid decompression means is controlled such that a calculation valuecalculated based on outputs of said first refrigerant conditiondetection means, said second refrigerant condition detection means, saidthird temperature detection means, and said fourth temperature detectionmeans become a target value.
 3. A refrigerant cycle apparatuscomprising: at least a compressor, a radiator, decompression meanscapable of changing an open degree, a heat absorber, an internal heatexchanger that performs heat exchange between a refrigerant at an outletof said radiator and the refrigerant at an outlet of said heat absorber,wherein first temperature detection means for detecting a refrigeranttemperature between an outlet of said compressor and an inlet of saidradiator and second temperature detection means for detecting therefrigerant temperature between an outlet of said radiator and ahigh-pressure side inlet of said internal heat exchanger are provided,and an opening degree of said decompression means is controlled suchthat a temperature difference (ΔT) between a detection temperature bysaid first temperature detection means and the detection temperature bysaid second temperature detection means becomes a target value.
 4. Therefrigerant cycle apparatus of claim 3 further comprising: thirdtemperature detection means for detecting an inlet temperature of amedium to be heated and fourth temperature detection means for detectingan outlet temperature of the medium to be heated, wherein the openingdegree of said decompression means is controlled such that a calculationvalue calculated based on outputs of said first temperature detectionmeans, said second temperature detection means, said third temperaturedetection means, and said fourth temperature detection means, instead ofsaid temperature difference (ΔT), become a target value.
 5. Arefrigerant cycle apparatus comprising: at least a compressor, aradiator, decompression means capable of changing an open degree, a heatabsorber, an internal heat exchanger that performs heat exchange betweena refrigerant at an outlet of said radiator and the refrigerant at anoutlet of said heat absorber, wherein first temperature detection meansfor detecting a refrigerant temperature between an outlet of saidcompressor and an inlet of said radiator and second temperaturedetection means for detecting the refrigerant temperature between theoutlet of said radiator and a high-pressure side inlet of said internalheat exchanger, third temperature detection means for detecting an inlettemperature of a medium to be heated and fourth temperature detectionmeans for detecting the outlet temperature of the medium to be heatedare provided, and an opening degree of said decompression means iscontrolled such that a sum (ΣΔT) of a temperature difference (ΔT1)between a detection temperature by said first temperature detectionmeans and the detection temperature by said fourth temperature detectionmeans and the temperature difference (ΔT2) between the detectiontemperature by said second temperature detection means and the detectiontemperature by said third temperature detection means becomes a targetvalue.
 6. A refrigerant cycle apparatus comprising: at least acompressor, a radiator, decompression means capable of changing an opendegree, a heat absorber, an internal heat exchanger that performs heatexchange between a refrigerant at an outlet of said radiator and therefrigerant at an outlet of said heat absorber, wherein firsttemperature detection means for detecting a refrigerant temperaturebetween an outlet of said compressor and an inlet of said radiator andsecond temperature detection means for detecting the refrigeranttemperature between the outlet of said radiator and a high-pressure sideinlet of said internal heat exchanger, third temperature detection meansfor detecting an inlet temperature of a medium to be heated and fourthtemperature detection means for detecting an outlet temperature of themedium to be heated are provided, and an opening degree of saiddecompression means is controlled such that a difference (ΔT1−ΔT2)between a second temperature difference (ΔT1) between a detectiontemperature by said first temperature detection means and the detectiontemperature by said fourth temperature detection means and a thirdtemperature difference (ΔT2) between the detection temperature by saidsecond temperature detection means and the detection temperature by saidthird temperature detection means becomes a target value.
 7. Arefrigerant cycle apparatus comprising: at least a compressor, aradiator, decompression means capable of changing an open degree, a heatabsorber, an internal heat exchanger that performs heat exchange betweena refrigerant at an outlet of said radiator and the refrigerant at anoutlet of said heat absorber, wherein first pressure detection means fordetecting a refrigeration pressure between at least an outlet of saidcompressor and an inlet of said decompression means and secondtemperature detection means for detecting a refrigeration temperaturebetween the outlet of said radiator and a high-pressure side inlet ofsaid internal heat exchanger are provided, and an opening degree of saiddecompression means is controlled such that a calculation valuecalculated based on a detection pressure by said first pressuredetection means and a detection temperature by said second temperaturedetection means becomes a target value.
 8. A refrigerant cycle apparatuscomprising: at least a compressor, a radiator, decompression meanscapable of changing an open degree, a heat absorber, an internal heatexchanger that performs heat exchange between a refrigerant at an outletof said radiator and the refrigerant at an outlet of said heat absorber,wherein second temperature detection means for detecting a refrigeranttemperature between an outlet of said radiator and a high-pressure sideinlet of said internal heat exchanger and internal heat exchanger outlettemperature detection means for detecting the refrigerant temperaturebetween a high-pressure side outlet of said internal heat exchanger andan inlet of said compression means are provided, and an opening degreeof said decompression means is controlled such that a temperaturedifference (ΔThx) between a detection temperature by said secondtemperature detection means and the detection temperature by saidinternal heat exchanger outlet temperature detection means becomes atarget value.
 9. The refrigerant cycle apparatus of claim 1, whereinsixth temperature detection means for detecting the refrigeranttemperature between a low-pressure side outlet of said internal heatexchanger and an inlet of said compressor is provided, superheat degreeof a compressor suction part is calculated from a refrigerant saturationtemperature at a detection point of said sixth temperature detectionmeans and a detection temperature by said sixth temperature detectionmeans, and the opening degree of said decompression means is controlledsuch that said superheat degree becomes the target value.
 10. Therefrigerant cycle apparatus of claim 9, wherein second pressuredetection means is provided between the low-pressure side outlet of saidinternal heat exchanger and the inlet of said compressor and saidrefrigerant saturation temperature is calculated based on a detectionvalue of said second pressure detection means.
 11. The refrigerant cycleapparatus of claim 9, wherein fifth temperature detection means isprovided between the inlet of said heat absorber and the low-pressureside inlet of said internal heat exchanger and said refrigerantsaturation temperature is calculated based on the detection temperatureof said fifth temperature detection means.
 12. The refrigerant cycleapparatus of claim 9, wherein a priority is given to control saidsuperheat degree over said temperature difference.
 13. The refrigerantcycle apparatus of claim 1, wherein said radiator is a heat exchangerthat exchanges heat with water.
 14. The refrigerant cycle apparatus ofclaim 1, wherein carbon dioxide is used as a refrigerant.
 15. Therefrigerant cycle apparatus of claim 5, wherein sixth temperaturedetection means for detecting the refrigerant temperature between alow-pressure side outlet of said internal heat exchanger and an inlet ofsaid compressor is provided, superheat degree of a compressor suctionpart is calculated from a refrigerant saturation temperature at adetection point of said sixth temperature detection means and adetection temperature by said sixth temperature detection means, and theopening degree of said decompression means is controlled such that saidsuperheat degree becomes the target value.
 16. The refrigerant cycleapparatus of claim 6, wherein sixth temperature detection means fordetecting the refrigerant temperature between a low-pressure side outletof said internal heat exchanger and an inlet of said compressor isprovided, superheat degree of a compressor suction part is calculatedfrom a refrigerant saturation temperature at a detection point of saidsixth temperature detection means and a detection temperature by saidsixth temperature detection means, and the opening degree of saiddecompression means is controlled such that said superheat degreebecomes the target value.
 17. The refrigerant cycle apparatus of claim15, wherein second pressure detection means is provided between thelow-pressure side outlet of said internal heat exchanger and the inletof said compressor and said refrigerant saturation temperature iscalculated based on a detection value of said second pressure detectionmeans.
 18. The refrigerant cycle apparatus of claim 16, wherein secondpressure detection means is provided between the low-pressure sideoutlet of said internal heat exchanger and the inlet of said compressorand said refrigerant saturation temperature is calculated based on adetection value of said second pressure detection means.
 19. Therefrigerant cycle apparatus of claim 15, wherein fifth temperaturedetection means is provided between the inlet of said heat absorber andthe low-pressure side inlet of said internal heat exchanger and saidrefrigerant saturation temperature is calculated based on the detectiontemperature of said fifth temperature detection means.
 20. Therefrigerant cycle apparatus of claim 16, wherein fifth temperaturedetection means is provided between the inlet of said heat absorber andthe low-pressure side inlet of said internal heat exchanger and saidrefrigerant saturation temperature is calculated based on the detectiontemperature of said fifth temperature detection means.